The present invention relates to a method and an apparatus for the detection of slag co-flowing within a stream of molten metal, more particularly, in molten steels as they are being poured from metallurgical vessels.
As steel is being poured from converters, ladles or tundishes, a layer of slag lies on the surface of the molten metal. For metallurgical reasons, an effort is made to pour out as little slag as possible. In general, the following methods for preventing the outflow of slag are known:
In a ladle, the approximate point in time at which the slag can flow out is determined. For this purpose, the ladle is weighed in its empty and full state in order to determine the amount of molten metal remaining in each case. After the reading on the scale indicates that the amount of material has dropped to critical levels, the outflow of slag is determined visually by the operating personnel.
Aside from the fact that the detection of the remaining quantity of molten metal can be determined only very imprecisely, since it depends on the degree of erosion of the ladle lining, this method is cumbersome, especially if the pouring is done under a protective gas, which is generally the case with high-grade steels. This is because part of the shielding needs to be removed so that the pouring stream can be observed. This requires a considerable effort in terms of mechanical engineering and is also detrimental to quality.
In another method, visual monitoring is eliminated, the pouring being discontinued when a certain filling level in the ladle is reached.
This method is uneconomical, because a residue of molten metal always remains in the ladle and later needs to be melted down.